Fumikane Shimada, the author of Strike Witches, was also the conceptual creator and character designer of Sky Girls. That's why they look the same.
Strike Witches also conceptually predates Sky Girls, if you want to be nitpicky.
Magic circles were NOT started in fucking Nanoha. Such a claim is retarded.
In addition, the magic circles concept is hardly important to Strike Witches. They're just there to be neat and show that the process involves magic.
The Neuroi are based on modern and prototype Nazi aircraft. They're just black and alien-looking.
It's a pretty common concept. Again, not solely Yukikaze.
Just complain about the ridiculousness of the show, please.
That's at least a valid argument.